Tunnel-kiln construction



may 2E, T1929, T. G. Monoum I TUNNEL KILN CONSTRUCTION Filed July 30 1927 Patented May El, i929.,

TAINE Gr. MCDOUGAL, OF FLINT, MICHGAN, ASSIGNOR TO A C SPARK PLUG COM- PANY, 0F FLINT, MICHIGAN, A CORPORATIGN OF MICHIGAN.

TUNNEL-RILEY CONSTRUCTION.

Application led July 30,

rlhis invention relates to a method of heat treatment which may be used in various industrial processes, such as the baking of ceramic materials, and enameled articles and in the heat treatment of various metals. The disclosure in the present ease relates particularly to the treatment of ceramic articles.

A tunnel kiln is used in carrying out the process referred to. A continual train of the wares to he heat-treated is passed through this tunnel, in either a continuous or an interrupted progression. Upenings are provided in the central portion of the tunnel for `the introduction of the gaseous or liquid r fuel and it is in this part of the tunnel that combustion takes place. The central part of the tunnel is hereinafter referred to as the high temperature zone. The heated gases resulting from the combustion are passed out toward the end of the. tunnel into which 'the wares to be treated enter. As the entering wares gradually heatas they pass toward the high temperature Zone and as the heated gases cool as they come in contact with the gradually heating wares, it is obvious that i the preheating zone of the tunnel is progressively lower in temperature from thecentral high temperature Zone to the point where the heated gases pass out of the tunnel.

ln the heat treating of ceramic materials, it is highly important that the heating be gradual. Sudden or nonainiform heating may cause cracking or warping of the wares, thus producing an inferior or a valueless product. ln a kiln wherein the wares contact directly with the current of heated gases from the high temperature zone, the heating of the wares is not as uniform as could be desired. lllhe currents of the heated. gases are uneven in temperature, due to slight variations in the supply of fuel and air and in the draft.

lt is an object of this present invention to gradually and uniformly heat the entering train of wares. 'l accomplish this by providing a muiile of refractory material in the preheating section of the tunnel, so that a portion of the heat from the escaping heated gases must be conducted through the muftle to the wares. As the muftie must necessariiy change in temperature very slowly, the wares become heated at a' uniform rate by radiation from the inner walls of the muiile.

lt is a further object of my invention to make allowance for the different qualities of 1927. Serial No. 209,456.

different ceramic materials by providing means whereby a portionof the escaping heated gases can be passed directly through the inutile if desired.

@ther objects and advantages of the invention will appear in the course of the following description, taken in connection with the accompanying drawing and appended claims.

ln the drawing:

Figures l and la are complementary longitudinal views of my improved tunnel kiln, portions of the tunnel being formed in section. The figures show complementary sections of the same tunnel.

Figure 2 is a section on the line 2-2 of Figure la. The passage through the mulile is so shaped that there is some clearance between the walls and the ware at the entrance. The passage converges toward the inner end of the mtime, however, and there the clearance between the ware and the inner walls of the tunnel is as little as possible in order that a minimum amount of the heated gases may enter the muiiie.

The tunnel is arched at the juncture of the high temperature and preheating zones, as illustrated at 22. This added clearance per* mits the escaping heated gases to pass through the space surrounding the muiiie instead of through the muflie itself.

The structure andconformation of the high 'temperature zone B and the cooling zone Gis the same as that described in my copending application Serial No. 75,046 filed December 12th, 1925, and reference may be had thereto for further details. lt is deemed suiicient for the purposes of the present application to state that aft-er heating in the high tempera.- ture zone B, the wares pass through the indirectly air-cooled section 24E and the indirectly water-cooled section 26 and thence out of they tunnel in the usual manner.

rlihe drafts may be controlled and varied in any desired manner. 4lin case it is desired to pass a current of the heated gases through the mue, one ormore of the top plates 28 may be removed.

rlihe structure described gives a uniform application of heat to the wares. During operation, the mue becomes heated'from the hot gases coming from the high temperature zone and heatis radiated to the wares. The heating is gradual due to the fact that the ware is spaced farther from the inner walls of the f Il' am niuiie at the entering end than it is at the end adjacent the high temperature zone and due also to the fact that the temperature of the niuiile is progressively lower from the high temperature zone toward the entering end. The inuie protects the Wares from the uncertain drafts and Currents of the heated gases and radiates heat at a uniform rate to the Wares.

ll elaiin:

l. lin a tunnel kiln, a heating and a preheating zone, means for supplying heat to said heating zone, a inutiie of refractory material Within said preheating Zone, means for passing wares through said preheating and heating zones, the walls of said Inuiie being converged toward the end adjacent the heating zone.

2. In a tunnel kiln, a heating and a preheating Zone, means for supplying heat to said heating Zone, a inuiiie ot' refractory material Within said preheating zone, said preheating zone being enlarged adjacent the inner entrancev to said niuille, and ineans for passing Wares through said preheating and heating zones.

in a tunnel kiln, a heating and a preheating zone, means for supplying heat to said heating Zone, a inutlie ot refractory material Within said preheating zone, means for main- Lfziaeaa taining a current of heated gases from said heat-ing zone and out through said preheating zone, the top of said niuftle being removable adjacent the eXit for the heated gases whereby a variable current of heated gases may be passed directly through the niuile, andh means for passing Wares through said pr` heating and heating Zones.

4. A tunnel kiln for burning Ceramic wares consisting of a preheating zone, a heating Izone, and a cooling Zone, means for Cireulating hot combustion gases about the wares in the heating zone, said preheating zone being provided With'a inutile completely shutting Off the hot gases from the wares so as to effect more gradual heating thereof.`

5. ln the combination as defined in claiin 4f, said preheating zone being enlarged adjacent. the inner end of the muiie.

6. A tunnel kiln for burning eeraniic wares consisting of a preheating zone, a heating Zone, and a` cooling Zone, ineans for circulating hoteoinbustion gases aboutthe Wares in the heating zone, said preheating zone being provided with means for completely enclosing the wares in their passage therethrough to prevent the direct projection of hot gases thereon.

TAINE G. MCDUUGAL. 

